Obesity is associated with impaired controls of glucose and lipid metabolisms. However, the molecular events leading to these metabolic defects are not well understood. In particular, it has been long recognized that both insulin receptor (IR) activity and fatty acid oxidation are impeded in the muscle of obese subjects by an indefinite mechanism. Our preliminary data show that IR interacts with a novel GTPase phosphoinositide 3- kinase enhancer-A (PIKE-A) to fully activate its kinase activity during insulin stimulation. This interaction is a metabolically regulated process as less IR/PIKE-A complex is founded in the skeletal muscle of obese mice and lipid-stimulated myotubes. We also found that genetic ablation of PIKE resulted in augmented AMP- activated protein kinase (AMPK) activation and lipolysis in muscle, thus protected the animals from diet- induced obesity and diabetes. Moreover, we observed an enhanced association between PIKE-A and AMPK in the skeletal muscle of diet-induced obese mice. Therefore, the interaction between PIKE-A, IR and AMPK may represent a novel regulation on lipid oxidation and insulin sensitivity, which is ravaged in the obese muscle. As a part of our long term goal to reveal the molecular mechanisms leading to various obesity-related disorders, we set forth the following studies to delineate the role of IR/PIKE-A/AMPK interaction in obesity-induced muscular insulin resistance and defective lipid oxidation. In this project, we will (1) characterize the molecular and functionl details of IR, PIKE-A and AMPK associations; (2) determine the mechanisms that regulate the IR/PIKE-A and PIKE-A/AMPK complexes formation with a special focus on lipotoxicity and inflammatory cytokines; and (3) study the obesity-induced pathology in muscle-specific PIKE knockout mice to demonstrate the critical role of IR/PIKE-A/AMPK interplay in energy and glucose homeostasis. Taken together, our proposed studies will provide a new mechanism to explain the alteration of insulin signaling and lipid metabolism in obese tissues, which is helpful to advance our understanding on the pathophysiology of obesity and improve the therapeutic design for its complications.